"Why... why did you hurt my brother when my brother called you for help? He was calling out for help," said Pigeon’s sister, Tesina Halbert.

Halbert said her brother had struggled with depression and anxiety and police had dealt with him before in a mental health capacity.

"If you knew you were already going to the scene to help someone you've transported previously, why it was handled in this manner?" Halbert said.

"When asked why he fired his weapon, he said 'He had a knife in his hand' and 'I felt like my life was in danger,'" Prater said.

Prater said the body camera footage helped make his decision to file the second-degree murder charge.

"You see officers doing exactly the right thing almost every single time. This is one of those situations, though, where we've alleged that an officer crossed the line and in fact broke the law," he said.

"I am again relieved that there's going to be justice for my brother," Halbert said.

Halbert knows it’s too late for her brother, but she hopes this case will improve the way officers deal with people struggling with mental illness.

"I want some changes out of this so that no other family has to go through what we're going through," Halbert said.

Sweeney is being held in the Oklahoma County Jail without bond.

He is a nine-year veteran of the Oklahoma City Police Department who was involved in another fatal officer-involved shooting back in 2015.

The Fraternal Order of Police released this statement about the situation:

“Police officers are routinely placed in dangerous situations where they must quickly make life-or-death decisions. We caution citizens against jumping to conclusions until the facts are fully presented.

At this time, the FOP is not privy to the findings of the criminal investigation, and the video released today is only one piece of the puzzle. We hope to have more information about the particulars of this tragic situation soon.

The FOP will always support members who act in good faith under the policies of the Oklahoma City Police Department and the law.

We know these are trying times for Sgt. Sweeney and his family, and we’re here for them. We also offer our sympathy to Mr. Pigeon’s family and loved ones.”